Control logic for gas turbine engine fuel economy

ABSTRACT

A method of operating a multi-engine aircraft includes operating a first engine of the aircraft to provide motive power; and operating a second engine of the aircraft in a standby mode to provide substantially no motive power, a rotor of the second engine having an idle rotational speed in the standby mode, and in the standby mode, sequentially executing cycles, a given cycle of the cycles including: opening a set of variable guide vanes upstream a compressor section of the second engine, spiking a rate of a fuel flow to a combustor of the second engine, the spiking and the opening timed to increase a rotational speed of the rotor of the second engine to an upper threshold above the idle rotational speed of the rotor, and in response to the rotational speed reaching the upper threshold, at least substantially closing the set of variable guide vanes.

CROSS-REFERENCE

The present application claims the benefit of priority to U.S. PatentApplication No. 62/855,062, entitled “CONTROL LOGIC FOR GAS TURBINEENGINE FUEL ECONOMY”, and U.S. Patent Application No. 62/855,131,entitled “AIR SYSTEM OF MULTI-ENGINE AIRCRAFT”, both filed on May 31,2019, the contents of both of which are hereby incorporated hereinentirely.

TECHNICAL FIELD

The application relates to methods of operating an engine of amulti-engine aircraft.

BACKGROUND OF THE ART

Helicopters may have two or more engines powering a main rotor via acommon reduction gearbox, and each of the engines is typically sizedsuch that the power of each engine is greater than what is required bythe helicopter in cruise. Improving operating fuel efficiencies of suchmulti-engine systems is desirable.

SUMMARY

In an aspect, there is provided a method of operating a multi-engineaircraft having a first engine and a second engine operable to power theaircraft, the second engine having a rotor operable at a substantiallyconstant idle rotational speed resulting from a substantially constantidle fuel supply rate to a combustor of the second engine, comprising:operating the first engine of the multi-engine aircraft to providemotive power to the aircraft; and operating the second engine of themulti-engine aircraft in a standby mode to provide substantially nomotive power to the aircraft, and in the standby mode, sequentiallyexecuting cycles with respect to the second engine, a given cycle of thecycles including: in response to a rotational speed of the rotor of thesecond engine reaching a threshold below the substantially constant idlerotational speed, modulating a set of variable guide vanes upstream acompressor section of the second engine toward a fully open position, atleast in part concurrently with the modulating toward the open position,spiking a rate of a fuel flow to a combustor of the second engine, thespiking and the opening timed to increase a rotational speed of therotor of the second engine to a threshold above the substantiallyconstant idle rotational speed, and in response to the rotational speedreaching the upper threshold, modulating the set of variable guide vanestoward a fully closed position.

In some embodiments, the spiking the rate includes increasing the rateis to an upper supply rate, the increasing the rate is followed by thedecreasing the rate to a lower supply rate, the upper supply rate islower than a minimum fuel supply rate required for the second engine toprovide motive power to the aircraft and greater than the substantiallyconstant idle fuel supply rate required to maintain rotation of therotor at a substantially constant idle rotation speed of the engine, thelower supply rate is lower than the upper fuel supply rate, and themodulating the set of variable guide vanes toward the fully openposition is followed substantially immediately by the modulating the setof variable guide vanes toward the fully closed position.

In some embodiments, the lower supply rate is lower than thesubstantially constant idle fuel supply rate, and the upper supply rateis greater than the substantially constant idle fuel supply rate.

In some embodiments, the modulating toward the fully open positionincludes modulating to the fully open position and the modulating towardthe fully closed position includes modulating to the fully closedposition.

In some embodiments, the given cycle includes a breathing-in phasefollowed by a breathing-out phase, and the breathing-in phase includes:i) executing the modulating toward the fully open positionsimultaneously with at least part of the increasing the rate, followedby ii) the modulating toward the fully closed position simultaneouslywith at least part of the decreasing the rate.

In some embodiments, the breathing-out phase includes maintaining theset of variable guide vanes in the fully closed position.

In some embodiments, the breathing-out phase includes maintaining therate at the lower supply rate.

In another aspect, there is provided a method of operating multipleengines of an aircraft, comprising: operating a first engine of themultiple engines to provide motive power to the aircraft; and operatinga second engine of the multiple engines in a standby mode to providesubstantially no motive power to the aircraft, the operating the secondengine in the standby mode including maintaining rotation of a rotor ofthe second engine by sequentially executing cycles, each cycle of thecycles including: opening a set of variable guide vanes upstream acompressor section of the second engine from a closed position to anopen position, increasing at least in part simultaneously with theopening the set of variable guide vanes, increasing a supply rate of afuel flow to a combustor of the second engine from a lower supply rateto an upper supply rate, with the fuel flow reaching the upper supplyrate substantially simultaneously with the set of variable guide vanesreaching the open position, and substantially simultaneously with theset of variable guide vanes reaching the reaching the open position,moving the set of variable guide vanes to the closed position anddecreasing the supply rate of the fuel flow from the upper supply rateto the lower supply rate.

In another aspect, there is provided a method of operating amulti-engine aircraft, comprising: operating a first engine of themulti-engine aircraft to provide motive power to the aircraft; andoperating a second engine of the multi-engine aircraft in a standby modeto provide substantially no motive power to the aircraft, a rotor of thesecond engine having an idle rotational speed in the standby mode, andin the standby mode, sequentially executing cycles, a given cycle of thecycles including: opening a set of variable guide vanes upstream acompressor section of the second engine, spiking a rate of a fuel flowto a combustor of the second engine, the spiking and the opening timedto increase a rotational speed of the rotor of the second engine to anupper threshold above the idle rotational speed of the rotor, and inresponse to the rotational speed reaching the upper threshold, at leastsubstantially closing the set of variable guide vanes.

In some embodiments, the increasing the rate is to an upper supply rate,the increasing the rate is followed by the decreasing the rate to alower supply rate, the upper supply rate is lower than a minimum fuelsupply rate required for the engine to provide motive power to theaircraft and greater than a minimum constant fuel supply rate requiredto maintain rotation of the rotor at a substantially constant idlerotation speed of the engine, the lower supply rate is lower than theupper fuel supply rate, and the opening the set of variable guide vanesis followed by the closing the set of variable guide vanes.

In some embodiments, the lower supply rate is lower than a minimum fuelsupply rate required to maintain rotation of the rotor at asubstantially constant idle rotation speed of the second engine, and theupper supply rate is lower than a minimum fuel supply rate required forthe second engine to provide motive power to the aircraft and greaterthan the minimum constant fuel supply rate required to maintain rotationof the rotor at the substantially constant idle rotation speed of thesecond engine.

In some embodiments, the decreasing the rate is started substantiallyimmediately after an end of the increasing the rate, the closing the setof variable guide vanes is started substantially immediately after anend of the opening the set of variable guide vanes, the opening the setof variable guide vanes is simultaneous with at least part of theincreasing the rate, and the closing the set of variable guide vanes issimultaneous with at least part of the decreasing the rate.

In some embodiments, the given cycle includes a breathing-in phasefollowed by a breathing-out phase, and the breathing-in phase includes:i) the opening the set of variable guide vanes simultaneously with atleast part of the increasing the rate, followed by ii) the closing theset of variable guide vanes simultaneously with at least part of thedecreasing the rate.

In some embodiments, the breathing-out phase includes maintaining theset of variable guide vanes closed.

In some embodiments, the closing the set of variable guide vanesincludes completely closing the set of variable guide vanes, and thebreathing-out phase includes maintaining the rate at the lower supplyrate.

In some embodiments, the lower supply rate is a zero supply rate.

In some embodiments, the method further comprises monitoring a rotorspeed of the engine, and in response to the rotor speed decreasing to apre-determined sub-idle threshold during the breathing-out phase of agiven cycle of the plurality of cycles, terminating the breathing-outphase of the given cycle and starting the breathing-in phase of asequentially next cycle of the plurality of cycles.

In some embodiments, during the breathing-in phase of the sequentiallynext cycle, the increasing the rate to the upper supply rate startssubstantially immediately after the rotor speed reaches thepre-determined threshold during the breathing-out phase of the givencycle.

In some embodiments, during the breathing-in phase of the sequentiallynext cycle the opening the set of variable guide vanes starts at one of:i) a substantially same time as a start of increasing the rate, and ii)a pre-determined time after the start of increasing the rate.

In another aspect, there is provided a method of operating an engine ofa multi-engine aircraft, comprising: operating the engine through asequential plurality of cycles, a given cycle of the plurality of cyclesincluding a breathing-in phase followed by a breathing-out phase, thebreathing-in phase including: i) in response to a speed of a rotor ofthe engine being at a sub-idle threshold, opening a set variable guidevanes upstream an air compressor section of the engine and injecting afuel into a combustor of the engine to increase the speed to at leastapproximately a pre-determined upper threshold, and then ii) in responseto the speed reaching at the upper threshold, at least reducing a supplyrate of the fuel into the combustor and at least substantially closingthe set of variable guide vanes, the breathing-out phase includingmaintaining the set of variable guide vanes closed at least until thespeed drops from the pre-determined upper threshold to at leastapproximately the pre-determined sub-idle threshold.

In some embodiments, in the breathing-in phase of at least one repeatingcycle of the plurality of cycles, the at least reducing the rate startsbefore a start of the closing the set of variable guide vanes.

In some embodiments, in the breathing-in phase of at least one repeatingcycle of the plurality of cycles, the opening the set of variable guidevanes starts at least approximately simultaneously with the injectingthe fuel, and the injecting the fuel includes increasing a supply rateof the fuel into the combustor.

In some embodiments, the at least reducing the rate includes reducingthe rate to a zero supply rate.

In another aspect, there is provided a multi-engine aircraft,comprising: a first engine operable to provide motive power to theaircraft; a second engine operable to provide motive power to theaircraft; at least one controller operatively connected to the first andsecond engines and configured to operate the first engine in a sub-idlemode while operating the second engine in an active mode, the sub-idlemode including sequentially executing a plurality of cycles, a givencycle of the plurality of cycles including a breathing-in phase followedby a breathing-out phase, the breathing-in phase including: i)modulating a set of variable guide vanes upstream an air compressorsection of the first engine to an open position, and a fuel supply to acombustor of the first engine to an upper supply rate, followed by ii)modulating the set of variable guide vanes to a substantially closedposition, and the fuel supply to a lower supply rate that is lower thanthe upper supply rate, the breathing-out phase including maintaining theset of variable guide vanes closed.

In some embodiments, the at least one controller is configured to startthe modulating the fuel supply to the lower supply rate substantiallyimmediately after terminating the modulating the fuel supply to theupper supply rate, and to start the modulating the set of variable guidevanes to the closed position substantially immediately after terminatingthe modulating the set of variable guide vanes to the open position.

In some embodiments, the at least one controller is configured to switchoperation of the first engine from the sub-idle mode into an active modeof the first engine at any point in time during operation of the firstengine in the sub-idle mode.

In some embodiments, the modulating the fuel supply to the lower supplyrate followed by modulating the fuel supply to the upper supply rate ispart of spiking the fuel supply to the combustor of the first engine.

In some embodiments, the at least one controller is configured to startthe spiking at least substantially simultaneously with starting themodulating the set of variable guide vanes to the open position, and toterminate the spiking at least substantially simultaneously withterminating the modulating the set of variable guide vanes to the closedposition.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross sectional view of a gas turbine engine;

FIG. 2 is a schematic of two gas turbine engines and of an air system ofan aircraft, with both of the engines being active;

FIG. 3 is a schematic of the two gas turbine engines and of the airsystem of FIG. 2, with one of the engines being active and another oneof the engines being on standby;

FIG. 4 is a schematic of two gas turbine engines and of the air systemof the aircraft of FIG. 2, the air system being implement according toanother embodiment;

FIG. 5 is a schematic of two gas turbine engines and of the air systemof the aircraft of FIG. 2, the air system being implement according toyet another embodiment;

FIG. 6 is a schematic logic diagram showing a method implementedaccording to an embodiment of the present technology; and

FIG. 7 is a schematic logic diagram showing a method implementedaccording to another embodiment of the present technology;

FIG. 8 is a schematic showing a breathing cycle of the presenttechnology, when implemented with respect to the engine of FIG. 1;

FIG. 9 is a schematic showing the breathing cycle of FIG. 8 in moredetail;

FIG. 10 is a schematic logic diagram showing a method implementedaccording to an embodiment of the present technology; and

FIG. 11 is a schematic logic diagram showing a method implementedaccording to an embodiment of the present technology.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a gas turbine engine 10. In thisexample, the gas turbine 10 is a turboshaft engine 10 generallycomprising in serial flow communication a low pressure (LP) compressorsection 11 and a high pressure (HP) compressor section 12 forpressurizing air, a combustor 13 in which the compressed air is mixedwith fuel and ignited for generating an annular stream of hot combustiongases, a high pressure (HP) turbine section 14, and a lower pressure(LP) turbine section 15. The respective pairs of the compressor andturbine sections 11, 12, 14, 15 are interconnected via respectiveindependently rotatable low pressure and high pressure spools, orshafts. This arrangement enables, inter alia, the core flow andprocessing of air through the engine 10, which is received through anair inlet 16 and exhausted via an exhaust outlet 17 of the turboshaftengine 10.

The turboshaft engine 10 further includes a set of variable guide vanes18, 19 at an inlet of one or both of the compressor sections 11, 14. Inother words, relative to a direction of airflow through the core of theturboshaft engine 10, a set of variable guide vanes 18 may be providedupstream of the LP compressor section 11 to modulate airflow into the LPcompressor section 11. A set of variable guide vanes 19 may be providedupstream of the HP compressor section 12 to modulate airflow into the HPcompressor section 12 and to modulate a power output of the turboshaftengine 10. The HP compressor section 12 is sometimes referred to as the‘gas generator’ of the engine 10.

The turboshaft engine 10 may include a transmission 15′ driven by the LPturbine section 15 via the low pressure shaft and driving a rotatableoutput shaft 15″. In some embodiments, the transmission 15′ may vary aratio between rotational speeds of the low pressure shaft and the outputshaft 15″.

FIG. 2 schematically illustrates an aircraft 20, in this non-limitingexample a helicopter, having a first engine 10′, and a second engine10″. The technology as described herein may be implemented with respectto a prior art multi-engine helicopter, and therefore a particularhelicopter is not shown or described in detail. For simplicity, only thenon-conventional aspects of the present technology are described indetail in this document. In other embodiments, the aircraft 20 may be ofa different type, such as an airplane for example.

The engines 10′, 10″ are operable to provide motive power to theaircraft 20 via, for example, one or more conventional transmissionsystems, which include the transmission 15′ shown in FIG. 1, andconventional controls. In this embodiment, each of the engines 10′, 10″is substantially the same as engine 10 shown in FIG. 1 and describedabove. Therefore, only the first engine 10′ is described in furtherdetail. Parts of the second engine 10″ that correspond to parts of thefirst engine 10′ are labeled with the same numerals.

As shown schematically in FIG. 2, the first engine 10′ includes a firstbleed air conduit 22 and a second bleed air conduit 24, both of whichbleed compressed air from respective parts of the LP and HP compressorsections 11, 12 of the first engine 10′. In the present embodiment, thefirst bleed air conduit 22 includes a check valve 24′ and branches offinto supply bleed air conduits 23 downstream of the check valve. In thisembodiment, the second bleed air conduit 24 includes a check valve 24′and a check valve 24″. The second bleed air conduit 24 branches off intosupply bleed air conduits 25 at one or more locations that are fluidlyin between the check valves 24′, 24″. As shown, the check valves 24′,24″ are pointing toward each other, for purposes explained below.

The supply bleed air conduits 23, 25 deliver bleed air to varioussealing and lubrication systems of the first engine 10′. The particularnumber and configuration of the sealing systems may be any suitablenumber and configuration, and is therefore not described in detail. Thesupply bleed air conduits 23 and 25 may also provide bleed air forvarious other functions of the first engine 10′ and/or the aircraft.Examples of such functions include, but are not limited to, cooling ofturbines, maintenance of cabin pressure, operation of air systems, andpressurizing liquid tanks. Any suitable air piping and controlsarrangement may be used to provide for each particular combination ofthe functions provided for by the bleed air from the first and secondbleed air conduits 22, 24.

Still referring to FIG. 2, the first and second bleed air conduits 22,24 of the first engine 10′ fluidly converge/join into a common bleed airconduit 26. The common bleed air conduit 26 fluidly connects to acontrol valve 28. The control valve 28 may be any suitable one or morecontrol valves so long as it provides for the functionality described inthis document. The conduits 22, 23, 24, 25, 26 and valves 22′, 24′, 24″of the first engine 10′ are part of a bleed air system 27 of the firstengine 10′.

As noted above, in this embodiment, the bleed air system 27 bleedscompressed air, via conduits 22 and 24, from the LP compressor section11 and the HP compressor section 12 of the first engine 10′, andsupplies it to various parts of the first engine 10′ including bearingassemblies for sealing and intershaft for lubrication. It iscontemplated that the bleed air system 27 may have a differentcombination of functions and/or other functions. The rest of the bleedair system 27 may be conventional and is therefore not shown ordescribed in detail herein. Details of the bleed air system 27 that arenot shown or described herein may be conventional, and are omitted tomaintain clarity of this description.

As shown in FIG. 2, in the present embodiment, the bleed air system 29of the second engine 10″ is similar to the bleed air system 27 of thefirst engine 10′, described above. Therefore, to maintain simplicity ofthis description, the bleed air system 29 of the second engine 10″ isnot described in detail. Suffice it to say that parts of the bleed airsystem 29 of the second engine 10″ that correspond to parts of the bleedair system 27 of the first engine 10′ are labeled with the samenumerals. Each of the bleed air systems 27, 29 of the aircraft 20 issized and designed to provide all of its functions at least when theengine 10′, 10″ that has the bleed air system 27, 29 is in an “active”mode (i.e. providing motive power to the aircraft 20). However, asdescribed in more detail later in this document, each of the engines10′, 10″ in this embodiment is also configured to operate an idlingmode, and in some embodiments in a “sub-idle” mode while at leastanother one of the engines 10′, 10″ is in an active mode.

For the purposes of this document, the term “active” used with respectto a given engine means that the given engine is providing motive powerto the aircraft with which it is used. For the purposes of thisdocument, the terms “standby”, “idle” and “sub-idle” are used withrespect to a given engine to mean that the given engine is operating butis providing no motive power, or at least substantially no motive power,to the aircraft with which it is used, with the “sub-idle” operationbeing a particular type of standby operation according to the variousembodiments described in this document.

In the “sub-idle” mode, the engine 10′, 10″ operates at a power level atwhich the engine 10′, 10″ provides no motive power, or substantiallymotive power, to the aircraft 20. In at least some operating conditions,while in the sub-idle mode, and but-for the selective airinterconnection between the bleed air systems 27, 29 described below, agiven engine 10′, 10″ may not provide sufficient pressure and/or supplyrate of bleed air to its bleed air system 27, 29 in order to enable thatbleed air system 27, 29 to provide all of its intended functions.

For the purposes of this document, the term “self-sufficient” used withrespect to a given bleed air system of a given engine means that thegiven bleed air system of the given engine provides all of its intendedfunctions for the duration of the time during which it is called upon toprovide the functions. A given bleed air system of a given engine is not“self-sufficient” when one or more of the intended functions of thegiven bleed air system may be unavailable or unstable due to a lack ofbleed air pressure and/or bleed air supply rate provided by thecorresponding engine to the given bleed air system. The selective airinterconnection between the bleed air systems 27, 29 provides for“self-sufficient” of each of the bleed air systems 27, 29 when theengine 10′, 10″ having that bleed air system 27, 29 operates in asub-idle mode. A non-limiting embodiment of the selective airinterconnection according to the present technology is described next,in detail.

As shown in FIG. 2, the common bleed air conduit 26 of the second engine10″, similar to the common bleed air conduit 26 of the first engine 10′,fluidly connects to a control valve 28. The control valve 28 is operableby a controller of the aircraft 20 to selectively: i) fluidly connectthe common bleed air conduit 26 of the first engine 10′ to the commonbleed air conduit 26 of the second engine 10″, and ii) fluidlydisconnect the common bleed air conduit 26 of the first engine 10′ fromthe common bleed air conduit 26 of the second engine 10″, as illustratedby the internal structure of the control valve 28 schematically shown inFIG. 2. The control valve 28 may be actuated using any suitable actuatorof the engines 10′, 10″ and/or of the aircraft 20.

FIG. 2 shows a first in-flight, cruise, mode of operation of theaircraft 20 during which both engines 10′, 10″ are operating in anactive mode, and are therefore both providing motive power to theaircraft 20. In this operating condition, the bleed air system 27 of thefirst engine 10′ and the bleed air system 29 of the second engine 10″are both self-sufficient without a need to use the control valve 28.Reference is now made to FIG. 3, which shows a second in-flight, cruise,mode of operation of the aircraft 20 during which: i) the first engine10′ is “active” and is therefore providing motive power to the aircraft20, and ii) the second engine 10″ is operating in a sub-idle mode and istherefore not providing any material amount of motive power to theaircraft 20. In this operating condition (i.e. in the second in-flightmode of operation), the bleed air system 27 of the first engine 10′ isself-sufficient. On the other hand, depending on each particularembodiment of the engines 10′, 10″ and/or the aircraft 20 and/or on thecharacteristics of the particular sub-idle operation of the secondengine 10″, the bleed air system 29 of the second engine 10″ may or maynot be self-sufficient in the sub-idle mode.

For this reason, during the second in-flight mode of operation of theaircraft 20, the control valve 28 may be actuated by a suitablecontroller of the aircraft 20 to fluidly connect the common bleed airconduit 26 of the first engine 10′ to the common bleed air conduit 26 ofthe second engine 10″, to provide for an additional supply of bleed airfrom the bleed air system 27 of the first engine 10′ to the bleed airsystem 29 of the second engine 10″. The common bleed air conduit 26, thethroughput of the control valve 28, and the size of the bleed air system27 may be selected so as to provide enough of a flow and pressure of theadditional supply of bleed air to the bleed air system 29 so as toenable self-sufficient operation of the bleed air system 29simultaneously with self-sufficient operation of the bleed air system27, with the second engine 10″ being in sub-idle mode. Conventionalengineering principles may be used to provide for such sizing, to suiteach particular embodiment and/or application of the aircraft 20.

After the second engine 10″ is brought into an “active” state while thefirst engine 10′ is in an “active” state, the control valve 28 may beactuated by a suitable controller of the aircraft 20 to fluidlydisconnect the common bleed air conduit 26 of the first engine 10′ fromthe common bleed air conduit 26 of the second engine 10″, as shown inFIG. 2. After the first engine 10′ is put into a standby mode or asub-idle mode while the second engine 10″ is in an “active” mode, thecontrol valve 28 may be actuated by a suitable controller of theaircraft 20 to fluidly connect the common bleed air conduit 26 of thefirst engine 10′ to the common bleed air conduit 26 of the second engine10″.

The bleed air system 29 of the second engine 10″ may thereby providecompressed air to the bleed air system 27 of the first engine 10′.Similarly, the common bleed air conduit 26, the throughput of thecontrol valve 28, and the size of the bleed air system 29 may beselected so as to provide enough of a flow and pressure of theadditional supply of bleed air to the bleed air system 27 so as toenable self-sufficient operation of the bleed air system 27simultaneously with self-sufficient operation of the bleed air system29, with the first engine 10′ being in sub-idle mode. Self-sufficiencyof both of the bleed air systems 27, 29 of the aircraft 20 during allmodes of operation of the engines 10′, 10″ may thereby be provided.

Further, the sub-idle mode of operation as described herein has beendeveloped as a way to improve upon prior art methods of idle operationof one or more aircraft engines, and is therefore not part of the priorart as of the time of writing this description. However, the selectiveair interconnection of two or more engines of an aircraft as describedherein may be implemented in multi-engine aircraft, such as at leastsome helicopters, in which one or more of the engines are operable in aprior art idle mode. The bleed air systems 27, 29 of the engines 10′,10″ and the control valve 28 are part of an air system 30 of theaircraft 20. As described above, the air system 30 of the aircraft 20implemented according to the present technology may therefore providefor self-sufficient operation of at least one of the engines 10′, 10″and/or the engines' 10′, 10″ bleed air system(s) 27, 29 in at least someoperating conditions of the aircraft 20 in which at least some prior artengines and/or engine bleed air systems may not be self-sufficient.

Further according to the present technology, as shown in FIGS. 2 and 3for example, in the present embodiment, the check valves 24′ and 24″ areprovided in the bleed air conduits 24, downstream of the branching-outbleed air conduits 25. In this embodiment, this the branching-out bleedair conduits 25 may supply compressed air to at least some subsystems ofthe respective engines 10′, 10″. Each of the check valves 24′ and 24″ensures that when the engine 10′, 10″ having that check valve 24′, 24″is providing compressed air from its bleed air system 27, 29 to thebleed air system 27, 29 of the other engine 10′, 10″, the compressed airis provided from the air source corresponding to the bleed air conduit22 of that engine 10′, 10″. The check valves 24′ and 24″ therefore helpensure uncompromised self-sufficient operation of the subsystems of theone of the engines 10′, 10″ that may at a given time be providingcompressed air to the other one of the engines 10′, 10″. In someembodiments, the check valve 24′ and/or the check valve 24″ may beomitted.

The rest of the air system 30 that is not shown in the figures of thepresent application may be conventional and is therefore not describedin detail herein. Any suitable controls and any suitable control logicmay be used to provide for the functionality of the air system 30,and/or for various timings of actuation of the control valve 28 to suitthe various different operations of the aircraft 20.

Referring now to FIG. 4, an air system 40 of the aircraft 20, which isan alternative embodiment of the air system 30 is shown. The air system40 is similar to the air system 30, and therefore similar referencenumerals have been used for the air system 40. A difference of the airsystem 40 from the air system 30, is that air system 40 includes acontrol valve 41, a control valve 42, and an external compressed airsource 43 such as an auxiliary power unit (APU) and/or an air compressorfor example. The external compressed air source 43 may be anyconventional external compressed air source suitable for each particularembodiment of the engines 10′, 10″ and the aircraft 20.

The control valve 41 selectively fluidly connects the externalcompressed air source 43 to the common bleed air conduit 26 of the firstengine 10′, via any suitable corresponding air conduits. Moreparticularly, when the first engine 10′ is “active”, the control valve41 may be actuated by a suitable controller of the aircraft 20 tofluidly disconnect the external compressed air source 43 from the commonbleed air conduit 26 of the first engine 10′, and may thereby allow thebleed air system 27 of the first engine 10′ to run self-sufficiently.

When the first engine 10′ is in a sub-idle mode according to the presenttechnology (further, simply “in a sub-idle mode”), or on “standby”according to prior art methods, the control valve 41 may be actuated bya suitable controller of the aircraft 20 to fluidly connect the externalcompressed air source 43 to the common bleed air conduit 26 of the firstengine 10′. The control valve 41 may thereby provide thatadditional/“supplemental” compressed air to the bleed air system 27 ofthe first engine 10′ at a supply rate and pressure sufficient to allowthe bleed air system 27 of the first engine 10′ to provide for all ofits intended functions during sub-idle or standby operation of the firstengine 10′. The control valve 41, via corresponding air conduit(s), mayselectively fluidly connect the external compressed air source 43 to adifferent part of the bleed air system 27 of the first engine 10′, solong as the functionality described above is provided.

The control valve 42 similarly fluidly connects the external compressedair source 43 to the common bleed air conduit 26 of the second engine10″, and is actuated according to a similar control logic to allow thebleed air system 29 of the second engine 10″ to provide for all of itsintended functions during sub-idle or standby operation of the secondengine 10″. As shown, the control valve 28 that fluidly connects thebleed air system 27 of the first engine 10′ to the bleed air system 29of the second engine 10″ may be in a position in which it fluidlydisconnects the first engine 10′ from the second engine 10″, to allowfor the supplemental compressed air to be provided to either one, or toboth, of the engines 10′, 10″ by the external compressed air source 43.In some embodiments, the control valves 28, 41, 42 may be actuatedcorrespondingly to switch between the various possible supply modes ofair described above. For example, in some operating conditions, thebleed air system 27, 29 of one of the engines 10′, 10″ may receive“supplemental” compressed air from one or both of: i) the bleed airsystem 27, 29 of another one of the engines 10′, 10″, and ii) theexternal compressed air source 43.

Referring now to FIG. 5, an air system 50 of the aircraft 20, which isyet another alternative embodiment of the air system 30 is shown. Theair system 50 is similar to the air system 40, and therefore similarreference numerals have been used for the air system 50. A of the airsystem 50 difference from the air system 40, is that air system 50 doesnot have a control valve 28 for fluidly connecting the bleed air system27 of the first engine 10′ to the bleed air system 29 of the secondengine 10″. Operation of the air system 50 is similar to operation ofthe air system 40 with respect to the external compressed air source 43.

In at least some embodiments and applications, the air systems 30, 40,50 may allow to provide “supplemental” compressed air to the bleed airsystem 27, 29 of one of the engines 10′, 10″ in at least some caseswhere that bleed air system 27, 29 is malfunctioning and/or leaking airfor example. A person skilled in the art will appreciate that while aparticular air conduit arrangement is shown in FIGS. 1 to 5, other airconduit arrangements may be used while providing for at least some ofthe functionality described in this document. While a single externalcompressed air source 43 is used in the embodiments of FIGS. 4 and 5,multiple different external compressed air sources may be used.Likewise, while the example aircraft 20 has two engines 10′, 10″, thepresent technology may be implemented with respect to more than twoengines and/or with respect to other types of engines.

With the above systems in mind, the present technology provides a method60 of using, in flight, a source of pressurized air external to anengine of an aircraft 20. As seen above, in some embodiments andoperating conditions, the source of pressurized air may be one of theengines 10′, 10″ of the aircraft 20, and in some embodiments, an APU 43or air compressor 43 of the aircraft 20. In some embodiments, the method60 includes a step 61 of operating a given engine 10′, 10″ of theaircraft 20 during flight. In some embodiments, the method 60 alsoincludes a step 62 of directing pressurized air from the source ofpressurized air external to the given engine 10′, 10″, to a bleed airsystem 27, 29 of the given engine 10′, 10″.

In some embodiments, the given engine 10′, 10″ to which pressurized airis directed is a first engine 10′ of the aircraft 20, the aircraft 20includes a second engine 10″, and the source of pressurized air externalto the first engine 10′ is a bleed air system 29 of the second engine10″. As seen above, in some embodiments, the aircraft 20 is amulti-engine helicopter in which the engines 10′, 10″ are operativelyconnected to drive at least one main rotor of the helicopter to providemotive power to/propel the helicopter.

As seen above, in some embodiments, the directing pressurized air to thebleed air system 27 of the first engine 10′ is executed when the firstengine 10′ is operating in a sub-idle mode on or standby. In embodimentsin which the source of the pressurized air is the bleed air system 29 ofthe second engine 10″, the second engine 10″ is active (i.e. providingmotive power to the helicopter). Similarly, in some operating conditionsduring flight, the given engine 10′, 10″ to which pressurized air isdirected is a second engine 10″ of the aircraft 20. In some such cases,the source of pressurized air external to the second engine 10″ is ableed air system 27 of the first engine 10′. In some such cases, thesecond engine 10″ is operating in a sub-idle mode or on standby whilethe first engine 10′ providing the compressed air is active (i.e.providing motive power to the helicopter).

As seen above, in some embodiments, the source of pressurized air is afirst source of pressurized air (e.g. first engine 10′ or second engine10″, depending on which of these engines is active and which is insub-idle operation or on standby), the aircraft 20 includes a secondsource of pressurized air (e.g. APU/air compressor 43 of the aircraft20). In some such embodiments, the second source of pressurized air 43is external to both the first engine 10′ and the second engine 10″. Insome such embodiments and in some flight conditions, the method 60comprises directing pressurized air from the second source ofpressurized air 43 to the first engine 10′. In some such embodiments andin some flight conditions, the method 60 comprises directing pressurizedair from the second source of pressurized air 43 to the second engine10″. Further in some such embodiments and in some flight conditions, themethod 60 comprises directing pressurized air from the second source ofpressurized air 43 to both the first engine 10′ and the second engine10″.

Further with the structure of the aircraft 20 described above, thepresent technology also provides method 70 of operating a bleed airsystem 27 of a first gas turbine engine 10′ of a multi-engine aircraft20 during flight. In some embodiments, the method 70 comprises a step 71of operating the first gas turbine engine 10′ of the aircraft 20 duringflight in a sub-idle or in a standby mode, such as an idle or a sub-idlemode that provides either no motive power or at least materially nomotive power to the aircraft 20. In some embodiments, the method 70comprises a step 71 of operating a second gas turbine engine 10″ of theaircraft 20 during flight in an active mode (i.e. providingnon-substantially-zero motive power to the aircraft 20).

In some cases, the steps 71 and 72 are executed simultaneously. In somesuch cases, the method 70 comprises directing pressurized air from ableed air system 29 of the second gas turbine engine 10″ to a bleed airsystem 27 of the first gas turbine engine 10′.

In some cases, the method 70 further includes a step 73 of operating asource of pressurized air (E.g. APU/air compressor 43, and the like) ofthe aircraft 20 external to both the first gas turbine engine 10′ andthe second gas turbine engine 10″, and a step of directing pressurizedair from the source of pressurized air 43 to at least one of the firstgas turbine engine 10′ and the second gas turbine engine 10″.

In some cases, the directing pressurized air from one of the bleed airsystems 27, 29 to the other one of the bleed air systems 27, 29(depending on which one of the bleed air systems 27, 29 requiressupplemental compressed air) may be executed simultaneously withdirecting pressurized air from a second source of pressurized air to theone of the bleed air systems 27, 29 that is receiving the supplementalcompressed air. In some embodiments, the second source of pressurizedair 43 includes, or is, at least one of: an APU 43 of the aircraft 20,and an air compressor 43 of the aircraft 20.

In some such cases, the air pressure in the one of the bleed air systems27, 29 receiving supplemental compressed air may be lower than thepressure of the supplemental compressed air. It is contemplated that anysuitable controls and control arrangements may be used to provide forthis pressure differential, where required. While two engines 10′, 10″of an aircraft 20 are described, it is contemplated that the presenttechnology could be implemented with regard to a larger number ofengines of an aircraft to provide supplemental compressed air from oneor more of the engines or other compressed air source(s), to one or moreother ones of the engines.

In at least some cases and in at least some embodiments, the technologydescribed above may be implemented with, and may help provide stablesub-idle operation of one or more engines of a multi-engine aircraft.Operating one or more of an aircraft's multiple engines in a sub-idlemode according to the present technology is described in detail next.

Referring to FIG. 8, the present technology provides a sub-idle mode 80of operation of an aircraft engine 10, 10′, 10″. The present embodimentof the sub-idle mode 80 is illustrated with respect to the engine 10 ofFIG. 1, but may be executed with regard to a different aircraft engineas well, such as one of the engines 10′ and 10″ of the aircraft 20described above.

Operating the engine 10 in sub-idle mode 80 according to the presenttechnology uses one or more of the rotor(s), such as corresponding onesof the shafts/compressors/turbines 11, 12, 14, 15, of the engine 10 asenergy accumulators, by varying the speed(s) of the rotor(s) of theengine 10 during repeating predetermined time intervals from a low to ahigh level, as described herein. It has been found by the developers ofthe present technology that the sub-idle mode 80 helps provide a loweroverall fuel consumption over a given operating time period incomparison with at least some prior art stand-by methods applied tosimilar sized/powered engines in at least some similar applicationsand/or operating conditions.

As shown in FIG. 8, in the present embodiment, the sub-idle mode 80includes a breathing-in phase 82 and a breathing-out phase 84, executedin a repeating sequence. In this embodiment, and although need not bethe case in other embodiments, the repeating sequential phases 82, 84are executed with respect to each of the rotors, and more particularlywith respect to both the rotor defined by the LP compressor and turbinesections 11 and 15, and the rotor defined by the HP compressor andturbine sections 12 and 14. In other applications and depending on theembodiment of a given engine with respect to which the method 80 may beapplied, the phases 82, 84 may be executed with respect to one or morebut not all of the rotors having a corresponding set of variable guidevanes upstream thereof. In some embodiments, the phases 82, 84 may beexecuted with respect to more than two rotors of a given engine, incases where each of the more than two rotors of the particular enginehas a corresponding upstream set of variable guide vanes. In someembodiments, and depending on the embodiment and-or application of agiven engine 10, 10′, 10″ and its one or more rotors, the phases 82, 84executed as described herein with regard to a given one of the rotor(s)of the engine 10, 10′, 10″ may have variations, such as differentmagnitudes and-or timings of the various parts of the phases 82, 84,relative to the phases 82, 84 executed with regard to a different one ormore of the rotors of that engine 10, 10′, 10″.

In the present embodiment, the breathing-in phase 82 includes opening,or open, the variable guide vanes 18, 19 at the air inlet 16 of theengine 10, and supplying fuel to the combustor 13 of the engine 10 whilecombustion is occurring therein or while initiating combustion, untilthe rotors 11, 12, 14, 15 have reached an upper pre-determined level ofkinetic energy. In some embodiments, the upper pre-determined level ofkinetic energy corresponds to a speed of the engine 10 at or above anidle speed of the engine 10.

Once the upper pre-determined level of kinetic energy is reached, abreathing-out phase 84 may be executed. As shown, the presentembodiment, the breathing-out phase 84 includes closing the variableguide vanes 18, 19 at the air inlet 16 of the engine 10 and reducingfuel flow to the combustor 13 of the engine 10 to at least one levelthat is below an idle speed of the engine 10. In some embodiments, thefuel flow is terminated during the breathing-out phase 84.

In an aspect, the closing of the variable guide vanes 18, 19 at the airinlet 16 during each breathing-out phase 84 limits entry of air into theengine 10 and thereby reduces drag and other losses at the rotors 11,12, 14, 15 of the engine 10. This helps conserve, for as long aspossible, the kinetic energy stored in the rotors 11, 12, 14, 15 as aresult of a sequentially preceding breathing-in phase 82. Rotating therotors 11, 12, 14, 15 of the engine 10 with the variable guide vanes 18,19 at the air inlet 16 being closed to restrict airflow through the airinlet 16 is referred to herein as a lower drag mode.

According to the present embodiment, the breathing-out phase 84 isexecuted until the kinetic energy in the rotors 11, 12, 14, 15 drops toa lower pre-determined level of kinetic energy, at which point asequentially next breathing-in phase 82 is executed to restore thekinetic energy to the upper pre-determined level for a sequentially nextbreathing-out phase 84. The breathing-in phases 82 and the breathing-outphases 84 are executed sequentially one after the other to provide forthe sub-idle mode 80 of operation of the engine 10. In an aspect, in atleast some embodiments and applications of the engine 10, the sub-idlemode 80 allows to reduce fuel consumed by the engine 10 over a giventime period, in comparison with prior-art idle operation methods that,for example, may run the engine 10 at a constant idle speed. In anotheraspect, in at least some embodiments and applications of the engine 10,the sub-idle mode 80 allows the engine 10 to respond quickly to a suddenpower demand stemming from the application in which the engine 10 isused.

Now referring to FIG. 9, the breathing-in phases 82 and thebreathing-out phases 84 of the sub-idle mode 80 of the presentembodiment are shown and described in more detail. As shown, thebreathing-in phases 82 all have one and the same VGV and fuel-flowprofile, and the breathing-out phases 84 all have one and the same VGVand fuel-flow profile. However, it is contemplated that in otherembodiments the breathing-in phases 82 and/or the breathing-out phases84 could each include more than one profile. More particularly, thebreathing-in phases 82 and the breathing-out phases 84 of the presenttechnology may be executed with respect to an engine 10, 10′, 10″ in asequential series of cycles 86, each of which may include a breathing-inphase 82 followed by a breathing-out phase 84. Executing a sequentialseries of the cycles 86 with respect to an engine 10, 10′, 10″ mayprovide for sub-idle operation of the engine 10, 10′, 10″ whichmaintains rotation of the engine's rotors 11, 12, 14, 15 and allows theengine 10, 10′, 10″ to be ready to quickly respond to a sudden demandfor motive power from that engine 10, 10′, 10″.

More particularly, with the above structure in mind and now referring toFIGS. 9 and 10, there is provided a method 88 of operating an engine 10,10′, 10″ of a multi-engine aircraft 20. In some embodiments, the method88 includes operating the engine 10, 10′, 10″ in a sub-idle mode, suchas the sub-idle mode shown in FIG. 9. As shown in FIG. 9, in someembodiments, the sub-idle mode includes, in response to a rotationalspeed of the rotors 11, 12, 14, 15 of the engine 10, 10′, 10″ reaching athreshold (LT) below a substantially constant idle rotational “MIRS”speed of the rotors 11, 12, 14, 15, which in some cases may be a ratedconstant idle rotational speed of the rotors 11, 12, 14, 15,opening/modulating a set of variable guide vanes, such as the set ofvariable guide vanes 18 and/or 19 shown in FIG. 1, upstream of one ormore air compressor sections, such as the LP compressor section 11and/or the HP compressor section 19, of the engine 10, 10′, 10″, towarda fully open position “OP”.

Also as shown in FIGS. 9 and 10, in some embodiments, the method 88includes executing, at least in part concurrently with the modulatingtoward the fully open position “OP”, increasing a supply rate (shown asthe slope of the fuel flow graph labeled “SR” in FIG. 9) of a fuel tothe combustor 13 of the engine 10, 10′, 10″ to an upper supply rate“UR”. As shown, in the present embodiment, the increasing the fuelsupply rate may be part of spiking the fuel supply rate from a sub-idlerate such as a lower supply rate “LR” (described below) to the uppersupply rate “UR” and at least substantially immediately upon reachingthe upper supply rate “UR”, reducing the fuel supply rate back to thelower supply rate “LR”. As shown, in some such embodiments, a rate ofthe increase may at least substantially equal a rate of the decrease.Also, as shown by the respective slopes of each vane 18, 19 opening andconcurrent fuel spiking phase mapped over a common time scale, andalthough this need not be the case in other embodiments, the spiking thefuel supply rate “SR” and the modulating the vanes 18, 19 may be timedfor the fuel supply rate “SR” to reach the peak sub-idle rate “UR” atleast substantially concurrently with the vanes 18, 19 reaching theirfully open position (shown at the peak of each given set of vanemodulation in FIG. 9).

As shown, in some such embodiments, the upper supply rate “UR” is lowerthan a minimum fuel supply rate “MRM” required for the engine 10, 10′,10″ to provide a material amount of motive power (or simply, “to providemotive power”) to the aircraft 20, and greater than a minimum constantfuel supply rate “CIR”, which may in some cases be a rated constant idlefuel supply rate of the engine 10, required to maintain rotation of therotors 11, 12, 14, 15 at the substantially constant idle rotation speed“MIRS” of the engine 10, 10′, 10″. The minimum fuel supply rate “MRM”,the minimum constant fuel supply rate “CIR”, and the substantiallyconstant idle rotation speed “MIRS” may be a function of each particularembodiment and type of engine 10, 10′, 10″ and/or the aircraft 20 and/orthe application with which the present technology is used, and may bedifferent and in at least some cases may be specified by themanufacturer(s) for each particular embodiment and type of engine 10,10′, 10″/aircraft 20/application.

In some embodiments, the method 88 includes closing/modulating theset(s) of variable guide vanes 18 toward a fully closed position “CL”,19, and decreasing the supply rate “SR” of the fuel to a lower supplyrate “LR” that is lower than the upper supply rate “UR”, to maintainrotation of the rotors 11, 12, 14, 15 of the engine 10, 10′, 10″. Asshown, in some embodiments, the lower supply rate “LR” is a zero supplyrate, meaning that the flow of fuel to the combustor 13 is shut off.However, in other embodiments and depending on the particular embodimentof the engine 10, 10′, 10″ for example, the lower supply rate “LR” is anon-zero supply rate, but is in at least some cases lower than theminimum constant fuel supply rate “CIR” required to maintain rotation ofthe rotors 11, 12, 14, 15 at the substantially constant idle rotationspeed “MIRS” of the engine 10, 10′, 10″.

Also as shown in FIG. 9, in each given breathing cycle 86, theincreasing the supply rate “SR” to the upper supply rate “UR” isfollowed by the decreasing the supply rate “SR” to the lower supply rate“LR”, and the opening/modulating the set(s) of variable guide vanes 18,19 toward the fully open position “OP” is followed by theclosing/modulating the set(s) of variable guide vanes 18, 19 toward thefully closed position “CL”. Yet further as shown in FIG. 9, in someembodiments in each given breathing cycle 86, the decreasing the supplyrate “SR” may be started substantially immediately after an end of theincreasing the supply rate “SR”, and closing/modulating toward the fullyclosed position “CL” (hereinafter, “closing”) the set(s) of variableguide vanes 18, 19 may be started substantially immediately after an endof the opening/modulating toward the fully open position “OP”(hereinafter, “opening”) the set(s) of variable guide vanes 18, 19.

Yet further as shown in FIG. 9, in some embodiments in each givenbreathing cycle 86, the opening the set(s) of variable guide vanes 18,19 is simultaneous with at least part of the increasing the supply rate“SR”, and the closing the set(s) of variable guide vanes 18, 19 issimultaneous with at least part of the decreasing the supply rate “SR”.Yet further as shown in FIG. 9, in some embodiments in each givenbreathing cycle 86, the breathing-out phase 84 includes maintaining theset(s) of variable guide vanes 18, 19 closed, and maintaining the supplyrate “SR” at the lower supply rate “LR”.

As shown, in some embodiments, in the sequentially-next breathing outphase 84, the set(s) of variable guide vanes 18, 19 are furthermaintained closed for a pre-determined time period after the start ofthe sequentially-next breathing out phase 84. In some embodiments, thistime delay is omitted, for example to suit a particular embodimentand/or application of the engine 10, 10′, 10″. In such embodiments,during the breathing-in phase 82 of a sequentially next breathing cycle86, the opening the set(s) of variable guide vanes 18, 19 starts at asubstantially same time as a start of increasing the supply rate “SR” offuel to the combustor 13.

In some embodiments, the method 88 further includes monitoring, forexample via the controller(s) 20′ and corresponding sensor(s), a rotorspeed “RS” (e.g. a relative rotational speed of the rotors 11, 12, 14,15 in one non-limiting embodiment) of the engine 10, 10′, 10″, and inresponse to the rotor speed “RS” decreasing to a pre-determined sub-idlethreshold “LT” during the breathing-out phase 84 of a given one of thebreathing cycles 86, terminating the breathing-out phase 84 of the givencycle 86 and starting the breathing-in phase 82 of a sequentially nextone of the breathing cycles 86. As shown, in some embodiments, duringthe breathing-in phase 82 of the sequentially next breathing cycle 86,the increasing the supply rate “SR” of fuel to the upper supply rate“UR” starts substantially immediately after the rotor speed “RS” reachesthe pre-determined sub-idle threshold “LT”, and thereby ensures that therotor speed “RS” does not materially drop below the pre-determinedsub-idle threshold “LT” speed.

In another aspect and now referring to FIG. 11, the present technologyfurther provides a method 100 of operating an engine 10, 10′, 10″ of amulti-engine aircraft 20, which includes operating the engine 10, 10′,10″ in a sequential plurality of breathing cycles 86, 86′ . . . 86 n,with each of the breathing cycles 86, 86′ . . . 86 n including abreathing-in phase 82 followed by a breathing-out phase 84 as describedabove. For clarity, only the breathing-in phase 82 and the breathing-outphase 84 of one of the breathing cycles 86, 86′ . . . 86 n is shown inFIG. 11 in detail.

In some embodiments of the method 100, a given breathing-in phase 82 mayinclude a step 102 of: i) in response to a speed of a gas generatorrotor 11, 12, 14, 15 (hereinafter, “rotor”) of the engine 10, 10′, 10″being at least approximately at a pre-determined sub-idle threshold“LT”, opening a set variable guide vanes 18 and/or 19 disposed upstreamof an air compressor section 11, 12 of the engine 10, 10′, 10″ andinjecting 104 a fuel into a combustor 13 of the engine 10, 10′, 10″ toincrease the speed to at least approximately a pre-determined upperthreshold “UT”, followed by a step 104 of ii) in response to the speedreaching at least approximately the pre-determined upper threshold “UT”,at least reducing a supply rate “SR” of the fuel into the combustor 13and closing the set of variable guide vanes 18 and/or 19.

In some such embodiments, a given breathing-out phase 84 may include astep 106 of maintaining the set of variable guide vanes 18 and/or 19closed at least until the speed of the rotor 11, 12, 14, 15 drops fromthe pre-determined upper threshold “UT” to at least approximately thepre-determined sub-idle threshold “LT”. In some such embodiments, in thebreathing-in phase 84 of at least one repeating breathing cycle 86 ofthe breathing cycles 86, the at least reducing the supply rate “SR”starts before a start of the closing the set of variable guide vanes 18and/or 19. In some such embodiments, in the breathing-in phase 82 of atleast one repeating breathing cycle 86 of the breathing cycles 86, theopening 102 the set of variable guide vanes 18 and/or 19 starts at leastapproximately simultaneously with the injecting the fuel into thecombustor 13, and the injecting the fuel includes rapidly increasing,and more particularly spiking, the supply rate of the fuel into thecombustor 13. In some such embodiments, the at least reducing 106 thesupply rate includes reducing the supply rate to a zero supply rate.

It is contemplated that particular timings, including starts and stops,of the steps, relative to each other, of the methods 88, 100 describedabove for each given engine 10, 10′, 10″ may be determined based onand/or dictated by each particular embodiment of that engine 10, 10′,10″ and/or that engine's 10, 10′, 10″ application, using for exampleconventional engineering and design methods.

Thus, now referring back to any one of FIGS. 1 to 5, the presenttechnology provides a multi-engine aircraft 20, such as a multi-enginehelicopter 20, that includes a first engine 10′ operable to providemotive power to the aircraft 20, a second engine 10″ operable to providemotive power to the aircraft 20, and at least one controller 20′operatively connected to the first and second engines 10′, 10″.

In some such embodiments, the controller 20′, which may be one or moresuitable controllers of the aircraft 20 and/or the engine(s) 10′, 10″for example, is configured to operate the first engine 10′ in a sub-idlemode while operating the second engine 10″ in an active mode (further,“first sub-idle configuration”). In some such embodiments, thecontroller 20′ is configured to operate the second engine 10″ in asub-idle mode while operating the first engine 10′ in an active mode(further, “second sub-idle configuration”), either in addition to orinstead of being configured to operate in the first sub-idleconfiguration. Since the first and second sub-idle configurations may besimilar, only the first sub-idle configuration is described in detailherein next.

Referring also to FIG. 9, operating the first engine 10′ in the sub-idlemode according to the present technology may include sequentiallyexecuting, by the controller(s) 20′, a plurality of breathing cycles 86,with each cycle 86 of the plurality of cycles 86 including abreathing-in phase 82 followed by a breathing-out phase 84. In someembodiments, the breathing-in phase 82 may include: i) modulating a setof variable guide vanes 18 and/or 19 in FIG. 1 upstream an aircompressor section 11, 12 of the first engine 10′ to an open position,and a fuel supply to a combustor 13 of the first engine 10′ to an uppersupply rate “UR”, followed by ii) modulating the set of variable guidevanes 18 and/or 19 to at least a substantially closed position, and thefuel supply to a lower supply rate “LR” that is lower than the uppersupply rate “UR”. In some embodiments, the breathing-out phase 84 mayinclude maintaining the set of variable guide vanes 18 and/or 19 atleast substantially closed, at least until a sequentially nextbreathing-in phase 82 for example.

In some embodiments, the modulating the set of variable guide vanes 18and/or 19 to the open position includes modulating the set of variableguide vanes 18 and/or 19 to at least a substantially open position. Insome such embodiments, the modulating the set of variable guide vanes 18and/or 19 includes modulating the set of variable guide vanes 18 and/or19 to a completely open position. In some embodiments, the closing themodulating the set of variable guide vanes 18 and/or 19 includescompletely closing modulating the set of variable guide vanes 18 and/or19. In some such embodiments, the maintaining the set of variable guidevanes 18 and/or 19 at least substantially closed includes maintainingthe set of variable guide vanes 18 and/or 19 completely closed.

As shown in FIG. 9, in some embodiments the at least one controller 20′is configured to start the modulating the fuel supply to the lowersupply rate “LR” substantially immediately after terminating themodulating the fuel supply to the upper supply rate “UR”, and to startthe modulating the set of variable guide vanes 18 and/or 19 to theclosed position substantially immediately after terminating themodulating the set of variable guide vanes 18 and/or 19 to the openposition.

This control logic may be said to provide for a “spiking” of the openingand closing the set of variable guide vanes 18 and/or 19, and for atleast a partially simultaneous “spiking” of the fuel supply rate. Insome such embodiments, the at least one controller 20′ is configured tostart the spiking the fuel supply rate at least substantiallysimultaneously with starting the spiking of the set of variable guidevanes 18 and/or 19, and to terminate the spiking the fuel supply rate atleast substantially simultaneously with terminating the spiking of theset of variable guide vanes 18 and/or 19. In some embodiments andapplications, the spiking of the fuel supply rate according to thepresent technology may reduce a rate of and/or a likelihood of fuelcoking in fuel manifold sections of the engine 10, 10′, 10″ beingoperated in a sub-idle mode of the present technology, in comparisonwith at least some prior art engine idling methods for example.

In some embodiments and such as where the aircraft 20 is a helicopterfor example, the at least one controller 20′ is configured to switchoperation of the first engine 10′ from the sub-idle mode into an activemode of the first engine 10′ at any point in time during operation ofthe first engine 10′ in the sub-idle mode. Similarly, in someembodiments, the at least one controller 20′ is configured to switchoperation of the second engine 10″ from the sub-idle mode into an activemode of the second engine 10″ at any point in time during operation ofthe second engine 10″ in the sub-idle mode. The at least one controller20′ may be therefore selectively operable between the first and secondsub-idle configurations described above.

In some embodiments and such as where the aircraft 20 is a single engineapplication for example, the breathing control logic and methodsdescribed herein may be used to reduce fuel consumption at differentstages of a given mission of the aircraft 20, such as an approach and adescent for instance, where no or almost no motive power is needed fromthe engine(s) 10′, 10″ of the aircraft 20. In some such applications,back-up systems and methods as described herein may be employed forexample to supplement one or more systems, such as a bleed air system 27for example, of the sub-idling engine(s) so as to ensure sustainedoperation of the system(s).

The particulars of how some of the functions described above are notdescribed in detail to maintain clarity of this description, because theparticulars may depend on each given embodiment of the aircraft 20 andthe controller(s) 20′ with which the present technology is implemented,and because the particulars may be implemented using suitablecorresponding conventional components of the aircraft 20 and usingsuitable conventional control methods.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the disclosed technology.

For example, in some embodiments, the sub-idling methods and technologydescribed herein may be implemented by using dedicated actuated panel(s)16′ (FIG. 1) disposed at or in the air inlet(s) 16 of an engine 10upstream of the compressor section(s) 11, 12, instead of or in additionto using the set(s) of variable guide vanes 18, 19. In some suchembodiments, the panel(s) 16′ may be configured to substantiallycompletely shut off airflow to the respective air inlet(s) 16 whenactuated to a closed position, and to substantially fully open the airinlet(s) 16 when actuated to an open position. Similar to the variableguide vanes 18, 19, actuation and control of the panel(s) 16′ may beexecuted using any suitable actuator(s), and using any suitablecontroller(s) of the engine 10 and/or the aircraft 20.

As yet another example, as shown in FIGS. 2-5 for example, in someembodiments, one or more of the air systems 30, 40, 50 may include oneor more pressure wave dampers 31, as described in the co-owned U.S.Patent Application entitled “AIR SYSTEM OF MULTI-ENGINE AIRCRAFT”, U.S.Patent Application No. 62/855,131, filed on May 31, 2019 and expresslyincorporated herein by reference. As stated in the 62/855,131application, in some embodiments, the air systems 30, 40, 50 may furthercomprise one or more pressure wave dampers 31 in air communication withone or more of the air pressure lines/conduits 22-26. A non-limitingexample of one of the pressure wave dampers 31 is shown in detail inFIG. 5. The term “pressure wave damper” as used herein includes alldevices that may in the present art be referred to as a pressure wavearrestor, pressure wave suppressor, pressure wave attenuator, and thelike, and their equivalents including one or more branch pipesconfigured to filter out one or more frequencies associated with theunwanted pressure waves. The pressure wave damper(s) 31 may absorband/or dampen and/or attenuate at least some of the pressurewaves/pulses/air pressure fluctuations/pulsations in the air pressureline(s)/conduit(s) 22-26 that may be generated during operation of theair systems 30, 40, 50, such as through executing the various methods60, 70 described above for example.

In at least some cases, like steady state operation, this may helpreduce a likelihood of standing wave resonances in the air systems 30,40, 50, and may help prolong an expected life cycle of the air systems30, 40, 50. In at least some embodiments, at least some of the pressurewave dampers 31 are made large enough to act as resonators during steadystate engine operation, thereby helping dissipate transient/surgepressure within the respective line(s) to which it/they are connected.For example, for effectiveness during a steady state operation, the neckdimensions (length and diameter) of a given pressure wave damper 31 maybe tuned to resonate with the accompanying volume of the given pressurewave damper 31 at the most prevalent excitation frequency and/or anEigen frequency of the corresponding air pressure line, to dissipateenergy that may be imparted to the air pressure line, for example as aresult of a control valve operation and/or a switchover of an enginefrom a standby mode to an active mode and/or vice versa, prior todistressing the air pressure line.

As shown, in some embodiments, the pressure wave damper(s) 31 may befluidly connected into the air systems 30, 40, 50 at locations proximateto one or more of the valves, for example valves 22′, 24′, 24″, 28, 41,42, of the air systems 30, 40, 50. Also as shown, in some embodiments,the pressure wave damper(s) 31 may be fluidly connected into the airsystems 30, 40, 50 at locations each of which may have been determinedto correspond to an air pressure maxima, and/or a maximum of a pressurewave inside the corresponding duct(s), pipe(s) or other air conduit(s),in the respective air system 30, 40, 50. Such positioning may helpfurther reduce a likelihood of, and in some embodiments and applicationsprevent, standing wave resonances in the air systems 30, 40, 50, and mayfurther help prolong life of the air systems 30, 40, 50.

More particularly, the air pressure maximums may be determined at one ormore switch-over conditions of the air systems 30, 40, 50, as describedabove (a.k.a. transient operation), during which the air systems 30, 40,50 may switch, for example: a) from supplying one of the engines 10′,10″ with supplemental compressed air to supplying another one of theengines 10′, 10″ with supplemental compressed air, or b) from notsupplying any supplemental compressed air to any of the engines 10′, 10″to supplying supplemental compressed air to at least one of the engines10′, 10″. More particularly, for a given air pressure line having acontrol valve, such as one or more of the control valves 28, 41, 42 forexample, the air pressure maximum, and/or the maximum of a pressurewave, may be calculated (e.g. by modeling) as a maximum air pressure inthe air pressure line when the control valve switches between one of: i)from fluidly blocking the air pressure line to fluidly unblocking theair pressure line, and ii) from fluidly unblocking the air pressure lineto fluidly blocking the air pressure line.

In some embodiments, one or more of the pressure wave damper 31 may be aHelmholtz resonator. In some embodiments, one or more of the pressurewave damper 31 may include a membrane/diaphragm that is fluidly and/ormechanically pressurized to enhance a frequency response of therespective air systems 30, 40, 50. In some embodiments, one or more ofthe pressure wave damper 31 may include a resonator volume that absorbsand/or attenuates and/or dissipates shockwaves and/or pressureoscillations and/or other aerodynamic instabilities. In some suchembodiments, the resonator volume(s) may be spherical, cylindrical, or a3D complex shape for example, and may be made sufficiently large todissipate transient/surge pressure within the respective air lines, toassist in mitigating stresses during the transient operations of the airsystems 30, 40, 50.

Also, in some embodiments, one or more of the pressure wave dampers 31may include a neck 32 (numbered in FIG. 2 only, to preserve clarity ofthe figures) that fluidly connects the resonator volume(s) to therespective air lines. In some such embodiments, the resonator neckdimensions, including a length and diameter thereof, may be selected toresonate with the corresponding resonator volume(s) at a prevalentexcitation frequency and/or at an Eigen frequency of the correspondingair line. In at least some cases, such dimensioning may help reducestresses experienced by the respective air systems 30, 40, 50 duringsteady state operation. Also, in some embodiments, such as where aHelmohltz resonator is used, the Helmohltz resonator may have an openinghaving an opening area (A), a neck with a length (L), and a volume (V).In such embodiments, the resonator frequency response of the Helmohltzresonator, or resonance, which may be tuned, may be expressed as thefollowing function: V=c0/2/pi*sqrt(A/V/L), where c0 is the velocity ofthe sound.

As yet another example, in the methods described above the vanes 18, 19in a first part of the breathing-in phases 82 are modulated to at leasta substantially open position. In some embodiments, and depending on theparticular embodiment of the engine 10 for example, one or more of thebreathing-in phases 82 may include opening the respective set(s) ofvanes 18, 19 to a position in a range of 70% to 100% of fully open. Insome embodiments, one or more of the breathing-in phases 82 may includeopening the respective set(s) of vanes 18, 19 to a position in a rangeof 70% to 90% of fully open. In some embodiments, one or more of thebreathing-in phases 82 may include opening the respective set(s) ofvanes 18, 19 to a position in a range of 80% to 90% of fully open. Insome embodiments, one or more of the breathing-in phases 82 may includeopening the respective set(s) of vanes 18, 19 to a position in a rangeof 90% to 100% of fully open.

As yet another example, in the methods described above the vanes 18, 19in a second part of the breathing-in phases 82 are modulated to at leasta substantially closed position. In some embodiments, and depending onthe particular embodiment of the engine 10 for example, one or more ofthe breathing-in phases 82 may include opening the respective set(s) ofvanes 18, 19 to a position in a range of 0% to 10% of fully open. Insome embodiments, one or more of the breathing-in phases 82 may includeopening the respective set(s) of vanes 18, 19 to a position in a rangeof 0% to 5% of fully open. In some embodiments, one or more of thebreathing-in phases 82 may include opening the respective set(s) ofvanes 18, 19 to a position in a range of 0% to 1% of fully open. In someembodiments, one or more of the breathing-in phases 82 may includeopening the respective set(s) of vanes 18, 19 to a position in a rangeof 1% to 2% of fully open. In some embodiments, one or more of thebreathing-in phases 82 may include opening the respective set(s) ofvanes 18, 19 to a position in a range of 1% to 4% of fully open. It willbe appreciated that in at least some cases, fully open and fully closedpositions of each given vane set 18, 19 may be different for differentembodiments of the corresponding engine and-or rotor(s) and-or may befor example modified to suit and-or optimize each particular embodimentof engine.

As yet another example, while the systems and methods described abovemay have been described individually, in some embodiments, one or moreof the systems and methods above may be used in combination with one ormore of the other systems and methods described above. In some suchcases, multiple different systems and methods may be implemented usingany suitable control system(s). As a non-limiting example, the systemsand methods described above, and-or combinations thereof, may beimplemented using any control systems, including controllers, sensors,actuators and the like, which may be for example conventional controlelements, which may be selected to suit each particular embodiment ofthe aircraft and engine(s) incorporating and using the systems andmethods. To maintain clarity of this description, such conventionalelements and details have not been described herein in detail. As anexample, the controllers described and shown above may be used toimplement the methods described above, and may be for example one ormore full authority digital controllers (FADEC).

Still other modifications than those given above as non-limitingexamples, and which fall within the scope of the present disclosure,will be apparent to those skilled in the art in light of a review ofthis disclosure.

The invention claimed is:
 1. A method of operating a multi-engineaircraft having a first engine and a second engine operable to power theaircraft, the second engine having a rotor operable at a substantiallyconstant idle rotational speed resulting from a substantially constantidle fuel supply rate to a combustor of the second engine, comprising:operating the first engine of the multi-engine aircraft to providemotive power to the aircraft; and operating the second engine of themulti-engine aircraft in a standby mode to provide substantially nomotive power to the aircraft, and in the standby mode, sequentiallyexecuting a plurality of cycles with respect to the second engine, agiven cycle of the cycles including: in response to a rotational speedof the rotor of the second engine reaching a threshold below thesubstantially constant idle rotational speed, performing a step ofmodulating a set of variable guide vanes upstream a compressor sectionof the second engine toward a fully open position, at least in partconcurrently with the modulating toward the fully open position,performing a step of spiking a rate of a fuel flow to the combustor ofthe second engine, the spiking and the modulating toward the fully openposition timed to increase the rotational speed of the rotor of thesecond engine to an upper threshold above the substantially constantidle rotational speed, and in response to the rotational speed reachingthe upper threshold, performing a step of modulating the set of variableguide vanes toward a fully closed position.
 2. The method of claim 1,wherein the spiking the rate includes a step of increasing the rate ofthe fuel flow to an upper supply rate, the increasing the rate of thefuel flow is followed by a step of decreasing the rate of the fuel flowto a lower supply rate, the upper supply rate is lower than a minimumfuel supply rate required for the second engine to provide motive powerto the aircraft and greater than the substantially constant idle fuelsupply rate required to maintain rotation of the rotor at thesubstantially constant idle rotation speed of the engine, the lowersupply rate is lower than the upper supply rate, and the modulating theset of variable guide vanes toward the fully open position is followedsubstantially immediately by the modulating the set of variable guidevanes toward the fully closed position.
 3. The method of claim 2,wherein the lower supply rate is lower than the substantially constantidle fuel supply rate, and the upper supply rate is greater than thesubstantially constant idle fuel supply rate.
 4. The method of claim 2,wherein the modulating toward the fully open position includesmodulating to the fully open position and the modulating toward thefully closed position includes modulating to the fully closed position.5. The method of claim 4, wherein the given cycle includes abreathing-in phase followed by a breathing-out phase, and thebreathing-in phase includes: i) executing the modulating the set ofvariable guide vanes toward the fully open position simultaneously withat least part of the increasing the rate of the fuel flow, followed byii) the modulating the set of variable guide vanes toward the fullyclosed position simultaneously with at least part of the decreasing therate of the fuel flow.
 6. The method of claim 5, wherein thebreathing-out phase includes maintaining the set of variable guide vanesin the fully closed position.
 7. The method of claim 6, wherein thebreathing-out phase includes maintaining the rate of the fuel flow atthe lower supply rate.
 8. The method of claim 7, wherein the lowersupply rate is a zero supply rate.
 9. The method of claim 8, furthercomprising monitoring the rotational speed of the rotor of the secondengine, and in response to the the rotational speed of the rotordecreasing to a pre-determined sub-idle threshold during thebreathing-out phase of the given cycle of the plurality of cycles,terminating the breathing-out phase of the given cycle and starting abreathing-in phase of a sequentially next cycle of the plurality ofcycles.
 10. The method of claim 9, wherein during the breathing-in phaseof the sequentially next cycle, the increasing the rate of the fuel flowto the upper supply rate starts substantially immediately after therotational speed of the rotor reaches the pre-determined sub-idlethreshold during the breathing-out phase of the given cycle.
 11. Themethod of claim 9, wherein during the breathing-in phase of thesequentially next cycle, the modulating the set of variable guide vanestoward the fully open position starts at one of: i) a substantially sametime as a start of increasing the rate of the fuel flow, and ii) apre-determined time after the start of increasing the rate of the fuelflow.